Midterm Study Guide Flashcards
what are the 2 basic advantages of hardness tests
simple and inexpensive
gives prediction of wear properties
non destructive
give idea of other proper ties such as tensile strength of metlas
what are 3 types of materials for which brinell test are not suitable and expaln reason for each type of material
coated materials- it doesnt calculate the coating but also the material inside
thin samples- since we are using high load, inaccurate reading may created if sample indents on other side.
very hard materials- it must be softer than the stell ball used or else it will cause ball damage
compare rock well b and c in terms of load, indenter and type of material the are used for
rockwell B-
load=100 kg
indenter=1/16’ steel ball
soft materials
Rockwell C
load=150 kg
120 degree diamond tipped
harder materials
explain why the sample size and thickness is important for hardness reading
sample should be thick enough about 10x the indent. there should not be indents on other side of sample this will cause inaccurate readings
sample size should be large enough so that we can test accurately over the entire sample. with allowing enough space between all the readings.
superficial tests are performed on ____ specimens. shore duometer is used when determining the hardness of ____
thin.
polymers
what is toughness
the amount of energy a material can absorb up to fracture, when rapid loads ahve been applied
what are static toughness and dynamic toughness
static- tensile test , with low strain
dynamic- rapid load, charpy, high strain
explain in detail why the titanic sank
at high temperature there was energy for the atoms to move but at lower temperature there was not enough energy for the atoms to move to have plastic deformation. Instead when the load is applied the material simply breaks.
explain why true stress value is higher than nominal stress value in tensile test
true stress accounts for change in crossectional area.
nominal stress uses the stress calculated in the beginning. it doesnt account for instaneous area change
what is necking
necking is when the area of the material begins to decrease due to an increasing constant force. on the graph it may appear that the stress is decreasing however it is increasing. because the test takes the begining area stress =f/A and not the Ai. this means it uses the formula on a smaller area giving an innacurate depiction of stress
expalin the difference between monomer and repeat unit
monomer- a molecule that bonds to other similiar molecules to for a polymer
repeat unit- is part of a polymer whose repetition forms a complete polymer
what are the means of amorphous, crystalline and semi crystalline? How does crystallinity affect tensile strength and elastic young’s modulus of a material?
amporous- polymer chains are disorderly packed
crystalline- polymer chains are packed tightly and orgainized
semi crystalline has both
more crystaliine=results in higher youngs modulus and tensile strength….. material is stronger due to chains being arranged in parralle, tightly packed arrangments
explain what glass transition temperature is and what materials exhibit this
glass transition - material become rubery
amphorous materials-semi crystalline-chains move and dont break, incrase energy added to system chains dont break but mobility goes up. thus rubbery state
polymers can be classified into 2 groups what are they
elastomers
plastics
